Custom Pest assertion to assert that a model has all the provided relations loaded, using the same dot syntax as with() and load()

Expectations.php

<?php

expect()->extend('toHaveLoadedRelations', function (array $relations) {
    $model = $this->value;
    $tested = [];

    expect($model)->toBeInstanceOf(Model::class, 'toHaveLoadedRelations expects a Model instance.');

    assert($model instanceof Model);

    foreach ($relations as $relation) {
        $parts = explode('.', $relation);
        $currentModel = $model;

        foreach ($parts as $index => $part) {
            $testing = implode('.', array_slice($parts, 0, $index + 1));

            if (! in_array($testing, $tested, true)) {
                expect($currentModel->relationLoaded($part))->toBeTrue("Expected relation $testing to be loaded.");

                $tested[] = $testing;
            }

            if ($index < count($parts) - 1) {
                $nextRelation = $currentModel->getRelation($part);

                if ($nextRelation instanceof Collection && $nextRelation->isEmpty()) {
                    note("The relation $testing is empty. Skipping to the next relation.");

                    continue 2;
                }

                $currentModel = $nextRelation instanceof Collection
                    ? $nextRelation->first()
                    : $nextRelation;
            }

        }
    }
})

Example:

Post::query()
    ->with([
        'images',
        'comments.replies',
    ])
    ->findOrFail(123);

// Assert relations loaded in test
expect($post)->toHaveLoadedRelations([
        'images',
        'comments.replies',
])